Radio transmission system



y 4, 1934. H. H. HIGGINBOTTOM 1,967,574

RADIO TRANSMISSION SYSTEM Filed Oct. 30, 1930 INVENTOR ATTORNEY Patented July 24, 1934 UNITED STATES PATENT OFFICE RADIO TRANSMISSION SYSTEM Application October 30, 1930, Serial No. 492,128

2 Claims.

This invention relates to transmission systems, and with particularity to methods and means of modulation.

An object of the invention is to provide a systern of modulation wherein distortion due to the coupling means is avoided.

A feature of the invention relates to a high frequency modulating system wherein the oscillator and modulator tubes are employed by means which has a minimum of frequency discrimination over an exceedingly wide range of frequencles.

Another feature of the invention relates to the combination of a high frequency oscillator and a modulating device coupled thereto through a resistance coupling.

Other features and advantages of the invention not specifically enumerated will be apparent after a consideration of the following detail de- 20, scription and the appended claims.

In certain types of transmission system such as television, picture transmission, etc., signals occupying a Very Wide frequency band are ordinarily required. This is particularly true in the case of television since the degree of detail and faithfulness of reproduction is intimately related to the capability of the system for transmitting the higher frequencies without attenuation or discrimination. In modulating systems as heretofore employed, the usual practice has been to use a low frequency choke coil to couple the modulator tube to the oscillator. It has been found that in the case of television transmission this type of coupling very seriously impairs the transmission of the higher frequencies, and also because of its low impedance at lower frequencies these low frequencies are reduced in response.

Accordingly, Fig. 1 of the drawing shows an improved type of modulating system wherein the entire frequency band is uniformly effective in modulation; and

Fig. 2 shows a modified manner of coupling the modulator to the oscillator in accordance with the invention.

Referring more particularly to Fig. 1, the numeral 1 represents an audion or electron discharge device of the grid control type. The input circuit comprising the grid 2, cathode 3, bias battery 4, and resistance 5 is connected to the sig- 15 naling device 6 which may take the form of a photo-electric cell. Associated with cell 6 is any type of television or picture transmission scanning system represented schematically by the numeral 7. The device 1 is connected so as to act as a modulator tube and this output circuit ineludes the anode 8, a coupling resistance 10, the anode supply 11 and the cathode 3. In the well known manner as the signaling device 6 is vari ably energized there result corresponding changes in potential across the resistance 10. Coupling resistance 10 is connected in common to the output circuit of the oscillator tube 12 through the high frequency choke coil 13 and regulating resistance 9. The input and output circuits of the oscillator 12 react upon each other through respective sections of the coil 14 to cause the generation of high frequency oscillations in the well known manner. The variations in potential drop across the resistance 10 are, therefore, impressed upon the anode 15 of the oscillator 12 to thereby vary the amplitude of the oscillations generated. Since the modulator 1 is coupled to the oscillator 12 through a substantially pure resistance coupling it has been found that there is very little if any frequency discrimination during the modulating process. It is therefore preferred to employ a resistance 10 of the non-inductive, noncapacitative type.

Fig. 2 shows a modified manner of coupling the modulator tube 1 with the modulator tube 12. In this embodiment the potential for anode 8 is applied through a resistance 16 which is separate from the resistance 17 through which the potential is applied to the anode 18. The variations in potential drop through the resistance 16 are impressed across the circuit including resistance 17, choke coil 19 and condenser 20. The impedance of the coupling circuit 19, 20 is preferably chosen so as to offer a minimum of impedance to the signaling frequencies, and at the same time to offer a relatively high impedance to the carrier frequency generated in the tube 12. Any type of signaling device represented schematically by the numeral 21 may be employed to energize the modulator tube 1. The remaining elements of the system shown in Fig. 2 are similar to those in Fig. 1, and further description thereof is not believed necessary.

What is claimed is:

1. In combination a source of television currents, an oscillator tube, a modulator tube, means for impressing said currents across the grid and cathode of the modulator tube, a direct current path between the anode and cathode of said modulator tube including in series a non-inductive resistance and a source of steady potential, said resistance having one end directly connected to the anode of the modulator tube, and the other end directly connected to the positive terminal of said source, another non-inductive resistance oscillator tube and to the cathode of the modulator tube, a condenser connecting the anode of the oscillator tube with the anode of the modulator tube, a connection from the positive terminal of said source through a non-inductive resistance to one side of said condenser, and a onnection fr m a po tiv erminal f said sour throug ano her non-indu tive r sistance t th other side of said condenser.

HAROLD H. HIGGINBOTTOM. 

